The basic goals remain the investigation of: (1) renal chloride handling as distinct from sodium; (2) the effects of changes in total body chloride and plasma chloride on renal function and acid-base balance; and (3) the role of anion in renin secretion. Firstly, the factors influencing and mechanisms underlying renal tubular chloride transport in the various nephron segments, including conservation of chloride by the distal nephron will be studied. This will include an analysis of the influence of extracellular fluid volume expansion and contraction, of changes in plasma chloride, and of other monovalent anions such as bromide and iodide in the tubular lumen on chloride reabsorption in the various segments of the nephron. Secondly, we will examine the effect of chloride depletion and hypochloremia, per se, on maintenance of extracellular fluid volume, acid-base status, segmental reabsorption, and urinary excretion of sodium, water, and chloride. The influence of acute and chronic chloride depletion on distal tubule and collecting duct chloride reabsorption will also be studied. Thirdly, the relationship between renal renin synthesis and release and delivery of sodium, and, especially, chloride to the distal tubule (macula densa) will be pursued. Experiments will be performed on rats. Techniques will include micropuncture and tubular radionuclide microinjection studies, metabolic balance, measurement of whole kidney, single nephron juxtaglomerular apparatus, and plasma renin, and determination of plasma and tissue electrolytes. We thus hope to further elucidate the important role of chloride in the renal control of fluid, electrolyte, and acid-base balance.